An image forming apparatus, such as a printing device and the like, that performs double sided printing to print image data on each of the front side and back side of a single medium is conventionally provided. Such an image forming apparatus includes a double sided printing unit. When the double sided printing is performed, a medium is supplied from a sheet supply tray that accommodates the medium. After performing the printing on one side of the medium, the medium is temporarily held in the double sided printing unit. The medium, on one side of which the printing has been performed, is subsequently supplied from the double sided printing unit to perform the printing on the other side of the medium (see JP Laid-Open Patent Application No. 2009-154540).
However, in the conventional image forming apparatus, to perform the double sided printing, the printing starts when page data for one side and page data for the other side of a single medium are present. Therefore, if the page data for both sides of the next medium is not present at a timing when a supply of a medium printed on a single side from the double sided printing unit is completed, the interval between the media, that is, a sheet distance extends greatly. Therefore, when the speed of the double sided printing and the speed of reading a document image by an image reading part are the same, for example, the sheet distance extends greatly until the number of pages of the generated page data catches up to the number of pages of the page data used for the double sided printing. This causes an excess operation of the image forming part and an increase in power consumption. In addition, this reduces the life of the consumable items, the device and the like.
The present application solves problems of the above-described conventional image forming apparatus and has an object to provide an image forming apparatus that suppresses the power consumption even during the double sided printing by monitoring the generated page data and a timing for starting the printing, thereby extending the life of the consumable items, the device and the like.